Midair collision avoidance system

ABSTRACT

A midair collision avoidance system (MCAS) employs an existing design of Traffic Alert and Collision Avoidance System (TCAS) as a module and seamlessly integrates it with a customized tactical module which is capable of providing unique tactical avoidance guidance control and display. The tactical module handles all phases of a tactical mission, including formation flight (e.g., formation fall-in, arming formation flight, engaging formation flight following, and formation break-away), and an air-refueling sequence (e.g., rendezvous, linkup, re-fueling, and disengaging air-refueling). The tactical module divides the air space around the aircraft into advisory, caution, and warning zones and for each provides display, tone and voice alerts to facilitate pop-up avoidance guidance commands. Military aircraft can thus effectively avoid mid air and near mid air collision situations in all three different operation modes: air traffic control (ATC) management mode, tactical mode, and a mixed mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/708,214, filed Nov. 8, 2000, entitled Midair Collision AvoidanceSystem now U.S. Pat. No. 6,278,396, which in turn was a continuation ofU.S. application Ser. No. 09/538,804 filed Mar. 30, 2000, entitled“Midair Collision Avoidance System” now U.S. Pat. No. 6,262,679, whichin turn was based on U.S. Provisional Application Serial No. 60/128,655,entitled “Midair Collision and Avoidance System (MCAS)” filed Apr. 8,1999.

TECHNICAL FIELD

The present invention relates generally to the field of avionics forairborne collision avoidance systems (CAS).

BACKGROUND OF THE INVENTION

Spurred by the collision of two airliners over the Grand Canyon in 1956,the airlines initiated a study of collision avoidance concepts. By thelate 1980's, a system for airborne collision avoidance was developedwith the cooperation of the airlines, the aviation industry, and theFederal Aviation Administration (FAA). The system, referred to asTraffic Alert and Collision Avoidance System II (TCAS II) was mandatedby Congress to be installed on most commercial aircraft by the early1990's. A chronology of the development of airborne collision avoidancesystems can be found in “Introduction to TCAS II,” printed by theFederal Aviation Administration of the U.S. Department ofTransportation, March 1990.

The development of an effective airborne CAS has been the goal of theaviation community for many years. Airborne collision avoidance systemsprovide protection from collisions with other aircraft and areindependent of ground based air traffic control. As is well appreciatedin the aviation industry, avoiding such collisions with other aircraftis a very important endeavor. Furthermore, collision avoidance is aproblem for both military and commercial aircraft alike. In addition, alarge, simultaneous number of TCAS interrogations from close-information aircraft members generate significant radio frequency (RF)interference and could potentially degrade the effectiveness ofmaintaining precise position/separation criteria with respect to otheraircraft and obstacles. Therefore, to promote the safety of air travel,systems that avoid collision with other aircraft are highly desirable.

Referring to FIG. 1, there is shown a block diagram of a conventionalTCAS system. Shown in FIG. 1 are TCAS directional antenna 10, TCASomni-directional antenna 11, and TCAS computer unit 12, which includesreceiver 12A, transmitter 12B, and processor 12C. Also shown are auralannunciator 13, traffic advisory (TA) display 14, and resolutionadvisory (RA) displays 15. Alternatively, the TA and RA displays arecombined into one display (not shown). The transponder is comprised oftransponder unit 16A, control panel 16B, and transponder antennas 16Cand 16D. The TCAS and transponder operate together to function as acollision avoidance system. Those skilled in the art understand thatthis is merely illustrative of a conventional TCAS. For example, manyother configurations are possible such as replacing omni-directionalantenna 11 with a directional antenna as is known to those skilled inthe art. The operation of TCAS and its various components are well knownto those skilled in the art and are not necessary for understanding thepresent invention.

In a TCAS system, both the interrogator and transponder are airborne andprovide a means for communication between aircraft. The transponderresponds to the query by transmitting a reply that is received andprocessed by the interrogator. Generally, the interrogator includes areceiver, an analog to digital converter (A/D), a video quantizer, aleading edge detector, and a decoder. The reply received by theinterrogator includes a series of information pulses that may identifythe aircraft, or contain altitude or other information. The reply is apulse position modulated (PPM) signal that is transmitted in either anAir Traffic Control Radar Beacon System (ATCRBS) format or in aMode-Select (Mode-S) format. Other replies are possible as is known tothose skilled in the art.

A TCAS II equipped aircraft can monitor other aircraft withinapproximately a 20-mile radius of the TCAS II equipped aircraft. (see,e.g., Brettner et al., U.S. Pat. No. 5,805,111, Method and Apparatus forAccomplishing Extended Range TCAS, which describes an extended rangeTCAS.) When an intruding aircraft is determined to be a threat, the TCASII system alerts the pilot to the danger and gives the pilot bearing anddistance to the intruding aircraft. If the threat is not resolved and acollision or near miss is probable, then the TCAS II system advises thepilot to take evasive action by, for example, climbing or descending toavoid a collision.

The TCAS II system, which is currently in operation on many commercialand military aircraft, is very effective in providing midair collisionavoidance in civil Air Traffic Control (ATC) airspace in determining therange, altitude, and bearing with other aircraft equipped with ModeS/ATCRBS transponders. It monitors the trajectory of these aircraft forthe purpose of determining if any of them constitute a potentialcollision hazard. The system is responsible for estimating the projectedintruder track and determining if a potential conflict exists. If aconflict is detected, the system displays an advisory to the pilot. Thesystem also provides guidance for vertical avoidance maneuver, known asResolution Advisories (RAs). Complementary avoidance maneuvers betweentwo TCAS equipped aircraft are ensured by automatic coordination ofmutual intentions with the other aircraft through the Mode Stransponders and associated TCAS.

However, the TCAS II (or other TCAS units) originally was not designedto handle unique mission capabilities, which would be required, forexample, by military aircraft. Examples of such unique missioncapabilities are: operate in a tactical environment (tactical speed anddynamic maneuvers), perform highly dynamic, close-in formation flight,rendezvous, and air refueling. At the same time, the system musteffectively detect and avoid midair collision situation.

SUMMARY OF THE INVENTION

The present invention comprises a hybrid midair collision avoidancesystem (MCAS), which can provide a comprehensive solution for mid aircollision avoidance and unique mission capabilities to perform formationflight, rendezvous, and air re-fueling. An aircraft equipped with thisMCAS can operate in many different environment modes, from a regulatedair traffic management (ATM) airspace to a tactical air space ofbattlefield, or a peripheral airspace having both ATM operational andtactical operational attributes.

The ATM module contains many existing core TCAS II functions, which canprovide traffic advisory (TA) and resolution advisory (RA) capabilitiesfor an aircraft to handle collision avoidance situation in the ATCairspace or environment. The ATM module is based on the latest TCAS IIsystem or equivalent which currently complies with the Federal AviationAdministration (FAA) Technical Standard Order (TSO)-C119a. The ATMmodule is easily upgradeable to incorporate any new requirement changesin order to be compliant with future ATM requirements.

To minimize the certification process for commercial TCAS relatedfunctions and to address specifically the operational capabilities ofaircraft, such as those used by the military aircraft, all of themissionized capabilities required to operate in a tactical environmentare allocated to the Tactical module. The tactical module works inconjunction with the ATM module to provide the following missionattributes: quick-time response, resistant to jamming and interference,and minimized detection beyond a short distance (e.g., 10 miles orless). The primary function of the Tactical module is to providetactical traffic alerts, tactical collision avoidance resolutions,display and control guidance to support unique mission capabilities suchas formation flight, rendezvous, and air refueling in a highly dynamicenvironment.

The novel features of the present invention will become apparent tothose of skill in the art upon examination of the following detaileddescription of the invention or can be learned by practice of thepresent invention. It should be understood, however, that the detaileddescription of the invention and the specific examples presented, whileindicating certain embodiments of the present invention, are providedfor illustration purposes only because various changes and modificationswithin the spirit and scope of the invention will become apparent tothose of skill in the art from the detailed description of the inventionand claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures further illustrate the present invention and,together with the detailed description of the invention, serve toexplain the principles of the present invention.

FIG. 1 is a block diagram of a conventional TCAS.

FIG. 2 is a block diagram of the midair collision avoidance system andits interfaces with other avionics systems and mission equipment onboard an aircraft in accordance with the present invention.

FIG. 3 is a block diagram of the air traffic advisory, collisionavoidance resolution, and proximity mission flight capabilities of theMCAS in accordance with the present invention.

FIG. 4 is a block diagram of a midair collision avoidance system (MCAS)in accordance with one specific illustrative embodiment showing modularpartition between the ATM module and the Tactical module, internal andexternal data communication, and the functional structure of the MCAS inaccordance with the present invention.

FIG. 5 is a logic flow diagram outlining the mode setting at initialsystem power-up and subsequent to power-up for the three system modes(ATM, tactical, or mixed) of operation of the MCAS system in accordancewith the present invention.

FIG. 6 is a mode transition diagram of the modes (ATM, tactical, ormixed) of operation of the MCAS system in accordance with the presentinvention.

FIG. 7 is a block diagram outlining user interfaces and tacticalcommunication protocols in accordance with the present invention.

FIG. 8 is a logic flow diagram outlining the intruder track filecorrelation process and blending sensor data process in accordance withthe present invention.

FIG. 9 is multi-dimensional space (proximity in closure time) of anexemplary time space region in which at least two aircraft are operatingin accordance with the present invention.

FIG. 10 is a logic flow diagram outlining a tactical collision avoidanceresolution process followed by MCAS to generate appropriate collisionavoidance maneuvering commands in accordance with the present invention.

FIG. 11 is vertical scanning profile (elevation versus) of an exemplarygeographical area illustrating the flightpath re-planning process inaccordance with the present invention.

FIG. 12 is a logic flow diagram outlining a formation flight processthat is followed by MCAS to provide formation flight commands inaccordance with the present invention.

FIG. 13 is a logic flow diagram outlining a rendezvous and air refuelingprocess followed by midair collision system to provide air-refuelingcommands in accordance with the present invention.

FIG. 14 is a block diagram outlining the Radio Frequency (RF)transmission power for the proximity flight mission of formation flightand air refueling in accordance with the present invention.

FIG. 15a is a display imagery frame illustrating an informationpresentation of tactical aircraft being complementary with ATM aircraftin an ATM mode in accordance with the present invention.

FIG. 15b is a display imagery frame illustrating a correlated trafficdisplay while separating in a mixed mode in accordance with the presentinvention.

FIG. 15c is a display imagery frame illustrating informationpresentation for a formation flight wingman while operating in atactical mode in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 2, there is shown a modularized structure diagram ofthe midair collision and avoidance system 18 along with other aircraftsystem. Typically, a military aircraft contains a number of avionicssystem connected to some kind of avionics bus 19 and mission equipmentconnected to some kind of mission bus 21. In conjunction with the midaircollision avoidance system (MCAS) 18, FIG. 2 shows a MCAS control panel30, a mode S/IFF (identification of friend or foe) transponder system32, digitized tactical data link system 34, airborne radar system 36,control display unit (CDU) 37, station keeping equipment (SKE) 37, datatransfer system (DTS) 38 which provides a digital terrain elevationdatabase, navigation system 40 comprised of an inertial navigationsubsystem (INS), a global position subsystem (GPS), an integratedcommunication system (ICS) 42, display systems 44 (e.g., VSI/TRA, EFIS,MFD, a head up display (HUD)), and a flight guidance control system 46.While these systems are exemplary of those attached to a typicalavionics bus 19 and mission bus 21, it will be understood that numerousother systems can be and typically are connected. Avionics bus 19 allowsall of the avionics on the bus to share information and communicate withone another. Mission bus 21 allows all of the mission equipment on thebus to share information and communicate with one another. A typicalexample of avionics 19 bus is an ARINC bus used in commercial ormodified commercial of the shell (COTS) applications. A typical exampleof a mission bus 21 is a MIL-STD-1553 bus used in military applications.

Midair collision avoidance system 18 provides conventional trafficadvisories, collision avoidance resolutions when the aircraft operatesin an air traffic control (ATC) environment (ATM mode). In the mixedmode, MCAS 18 provides display for tactical advisories, cautions, andwarning situations and responsive control guidance to match with a fastoperational tempo and the dynamics of the environment. In the tacticalmode, MCAS 18 provides unique mission capabilities to allow a militaryaircraft to perform formation flight following, to rendezvous with otheraircraft, and to dock with a tanker for air-refueling and avoidcollision with other electronically-coordinated aircraft. The system'stwo functional modules, ATM 20 and Tactical module 22 shown in FIG. 2,perform specific MCAS functions based on system mode in operation andwhich is determined by a set of parameters including operationalenvironment, digital data link capability, preset and manual input data,and MCAS mode selection.

When the aircraft is operating in an ATM mode. (pure ATM environment),then MCAS 18 is an onboard advisory system designed to act as a backupto the air traffic control (ATC) radar and the “see and avoid”principle. The system has a surveillance envelope defined by ahorizontal radius of approximately 40 nautical miles and an unlimitedvertical range. The system continually surveys the airspace around theaircraft, seeking replies from other aircraft ATC transponders. The ATMmodule 20 manages the replies of the transponder 32. Currently, flightpaths are predicted based on their tracks. Flight paths predicted topenetrate a potential collision airspace surrounding the MCAS 18aircraft are annunciated by MCAS. The ATM module 20 generates two typesof annunciations: Traffic Advisory (TA) and Resolution Advisory (RA).

When the aircraft is operating in a tactical mode, MCAS 18 activates thefunctions embedded in the Tactical module 22 to identify coordinatedtactical aircraft, provide display and voice indicative of tacticaladvisory, caution, warning, and generate control and guidance commandsfor the flight guidance system 46. An aircraft is defined as acoordinated aircraft if it is a formation leader, formation sub-leader,or a tanker. The preferred system processes pilot commands and activatesdedicated processes in the tactical module 22 to accommodate uniquemission capabilities needed by an aircraft for example, in a formationflight or an air re-fueling. Each dedicated process performs a completeset or subset of functions depending on the role of the aircraft in aformation flight or an air re-fuelling mission. The aircraft can beeither a formation leader, a formation sub-leader, a wingman, a tanker,or an air refueller.

When the aircraft is operating in a mixed mode (ATM and tactical), MCAS18 is not only an onboard advisory system, but also a mission controlguidance and display system. If the aircraft operates in a mixed mode,the MCAS 18 will have to process collision avoidance solutions (CAS) inparallel with tactical solutions. The MCAS 18 distributes intruder airtraffic tracking to different modules in order to generate appropriateTAs and RAs for tactical, coordinated tactical, unknown, andnon-tactical aircraft. If an intruder aircraft is a commercial aircraft,then the ATM module 20 will provide TAs and RAs according to the AirTraffic Management (ATM) rules. Conversely, if an intruder aircraft isany tactical aircraft type, then the tactical module 22 will use atactical model (e.g., FIG. 9) with specific timing constraints toproduce advisories, cautions, warning displays, audio tones and voice,and to process applicable control and avoidance guidance control lawsfor commands. The audio tone will be modulated with varied frequency toindicate the dangerous levels of proximity range and closure rate withan intruder aircraft. Voice messages are also provided to requestimmediate, specific pilot actions such as “CLIMB-CLIMB-CLIMB”,“DESCEND-DESCEND-DESCEND”, “INCREASE CLIMB”, “TURN LEFT”, “ROLL OUT”,“TURN RIGHT”, “REDUCE DESCENT-REDUCE DESCENT”, and other voice messagesto respond to the current air traffic and collision situation. Thetactical module 22 also controls radio frequency (RF) transmission powerlevel, manages the frequency of data transmission, and placestransmission source (e.g., transponder, VHF/UHF radios) in a standbymode based on the system mode, the aircraft's role in a mission, and thepilot's manual selection.

Referring to FIG. 3, there is shown various types of intruder equipmentand the resulting advisories. With respect to the air collisionavoidance capabilities, aircraft equipped with MCAS as shown in blocks45 and 46 have extensive traffic advisory and air collision avoidancecapabilities, that include ATM TAs and RAs, tacticalcaution/advisory/warning, and tactical avoidance solutions andresolutions 47. For example, the MCAS positioned as the wingman aircraftof a formation flight or in the refueller aircraft in an air refuellingmission will generate relative position deviation cues and velocitydeviation cues for display systems 44 and control commands to the flightguidance system 46 in FIG.2. The MCAS 18 responds with various CAScapabilities depending on the capability of intruder aircraft 49 a-d. Itshould be noted that Mode A only equipped intruders 48 will result indetection and display of TAs 49 d only. An intruder not equipped with atransponder is essentially invisible to MCAS unless it has a digitizedtactical data link.

Referring to FIG. 4, there is shown a more detailed block diagram of theMCAS 18 in FIG.2. Each module of the MCAS 18 contains a number ofcomponents, each of which provides a specific capability. While each ofthese components has dedicated functions, it will be recognized that, ineach module, they continue to communicate with one another and share theinformation at all times. Communication between the MCAS and Avionicsand Mission equipment onboard the aircraft is performed through missionand avionics dual bus input/output process 55. This process transmits,receives, and distributes MCAS related data to the two internal databus, ATM data bus 71 and tactical data bus 61. For the ATM based module20, the communication and data shared between its components isestablished through ATM data bus 71, a bus internal to this module 20.For the tactical based module 22, the communication and data sharedbetween its components is established through tactical data bus 61, abus internal to this module 22. Communication and data passing betweenthe two MCAS modules 20 and 22 are accomplished through ATM/Tacticalintra-communication bus 59. The real time data shared between the twomodules 20 and 22, not only includes MCAS system mode, user-input dataand selection, but also intruder track file data being processed,correlated, and maintained in each module. The shared intruder trackfile is used to resolve any ambiguities in terms of identifying anintruder aircraft as tactical, coordinated tactical, non-tactical(equipped with commercial TCAS) or unknown aircraft (detected byairborne radar system and by being not correlated in current trackfiles).

Included within the ATM module 20 is ATM mode control management 78, IFFtransponder and input/output process 70, ambiguity data correlationprocess 73, ATM based resolution advisory (RA) process 72, ATM basedtraffic advisory (TA) process 74, and display driver 76.

ATM mode control management process 78 coordinates data transmitting andreceiving with the mode S/IFF transponder 32, computations necessary todetermine traffic alerts and air collision avoidance conditions,intra-module communication, and track file correlations.

Ambiguity data correlation process 73 compares the following parameters:aircraft identification (ID), mission identification (MID), aircraftflight number, aircraft type, and aircraft position or relative position(distance, bearing, and pressure altitude) contained in each record ofthe intruder track file provided by IFF transponder with that providedby the Tactical module 22. This process identifies and tags intruderaircraft as a tactical aircraft if there is a match of at least two ormore correlated parameters listed above. Resulting from the ambiguitydata correlation process 73, the ATM module 20 processes ATM TAs and RAsfor all aircraft that have not been tagged as tactical in the mixedmode. In the ATM mode, the information of a tactical aircraft isprocessed for TAs and RAs just like any non-tactical aircraft, andpresented as a modified feature and color intruder symbol being overlaidthe on traffic situation awareness display.

ATM based traffic advisory process 74 determines traffic advisories toindicate range, bearing, and relative altitude of the intruder to aid invisual acquisition of the intruder. In the ATM mode, the system tracksall aircraft in the surrounding airspace and generates trafficadvisories (TAs) or resolution advisories (RAs), as the situationrequires. Vertical guidance to avoid midair collision is accomplished byinterrogating the Mode A, Mode C, and Mode S transponders of potentialthreat aircraft, tracking their responses, and providing advisories tothe flight crew to assure vertical separation. Two levels of advisoriesare provided: 1) traffic advisories indicating range, bearing, andrelative altitude of the intruder to aid in visual acquisition of theintruder; and 2) resolution advisories indicating what vertical maneuverneeds to be performed or avoided in order to assure safe separation.

ATM-based MCAS functions will generate both RAs and TAs when thetransponder is in Mode S operation. The two types of advisoriescorrespond to predefined time-based protection zones around theaircraft. The airspace around the MCAS aircraft, where a RA isannunciated, represents the warning area; while the larger airspace,which results in a TA being annunciated represents the caution area. Thewarning area is an airspace around the host aircraft with 20 to 35seconds closure time to collision. The caution area is an air spaceextended from the warning area by an additional 20 to 48 seconds.

ATM based in resolution advisory process 72 determines resolution forair collision conditions in advising the flight crew of a verticalmaneuver to take or avoid.

In conjunction with pilot selection, the traffic information, trafficalerts, and air collision avoidance resolution, display driver 76generate display images for local traffic situations and overlaidadvisory text messages and symbols.

If the system mode is set to either a tactical mode or a mixed mode,then MCAS performs many processes embedded in the Tactical module 22 andthese processes are described herein.

Included within the Tactical based MCAS functions' module 22 are MCAScontrol management 50, ATM and tactical data interface 52, tacticalcommunication protocols 51, MCAS mission and user data process 53,intruder track file correlation process 54, blending sensor data process56, display driver for display surfaces (e.g., NVS, MFD, and HUD) 68,tactical traffic alerts process 60, tactical collision avoidanceresolution process 58, formation flight advisory and guidance process62, rendezvous and air-refueling advisory and guidance process 64, RFpower transmission management 66, and MCAS voice and tone generationprocess 67.

MCAS control and management process 50 evaluates input data and pilotselections from control display unit (CDU), data transfer system (DTS),and MCAS control panel, along with the operational status of the variousdata link systems on board the aircraft to determine the active systemmode. One of the three main system modes, ATM mode 126 (FIG. 5) and 170(FIG. 6), Tactical mode 124 (FIG. 5) and 160 (FIG. 6), and Mixed mode128 (FIG. 5) and 170 (FIG. 6), will be set active as shown in FIG. 5 andFIG. 6.

ATM and tactical data interface 52 (FIG. 4) provides handshakes with theIFF transponder and bus I/O process 70, and perform the functions oftransmitting and receiving the shared data between two modules.

Tactical communication protocols 51 receives, processes, and distributesdigital communication data, specifically, dynamic CAS related data,received by the physical link layer (e.g.; VHF/UHF, or Integrated DataModem) connected with digitized tactical data link system 34. Theprocess 51 collects and formats MCAS data into packets to provide to thedigitized tactical data link for selectively broadcasting to otheraircraft. In conjunction with Mode S data link, the digitized tacticaldata link 34 will not only be used to broaden the reception bandwidthfor the MCAS related data, but also provide a reliable backup data linksource, particularly, in a tactical environment that possibly includesjamming and radio frequency (RF) interference. Military digitizedtactical data link capability for example, can be an important medium topipe in mission and navigation data from other military aircraft, ships,and ground vehicles. Many important features provided by direct datalink include secure data, robustness in terms of transmitting andrequesting to retransmit, built-in error correction, and datacompression from any of the used communication protocols. These includeJPEG or any selected tri-service communication protocol. The frequencyof transmit data link can be defaulted to a medium rate (6 Hertz) forthe sole purpose of tactical collision avoidance, and can be increasedto a higher rate (25 Hertz) in order to accommodate a tight formationflight and air-refueling operations. For instance, in a formationflight, tactical data link of the leader aircraft will be scheduled totransmit at a rate of 25 Hertz at a minimum power level to minimize longrange detection. If a fighter aircraft operates at a tactical speed orin a dynamic maneuvering environment, then the data link will also needto be operated at a higher rate. For a rendezvous mission, when twoaircraft are still far apart, the transmission can be set at a low rate,e.g., from 1 to 2 Hertz. The rate will switch to a higher rate as thetanker is approaching the rendezvous location.

A tactical data link packet would include of data regardinginstantaneous host aircraft but not limited to aircraft position, sourceof navigation, datum, navigation accuracy index, pressure altitude,radar altitude, velocity vector, acceleration vector, flightphase/maneuvering sequence events, control and guidance mode, andcontrol guidance target settings. Generally, all data is time taggedwith a precise universal time provided by the Global Position System(GPS) segment. Although some of the navigation dynamic data will beoverlapped with the data obtained from extended IFF Mode S transponder,the data provided by the tactical data link 34 serves as complementaryand backup unit in the computations required for tactical collisionavoidance solutions.

MCAS mission and user data process 53 pilot input data to the MCAS 18can be entered into the MCAS 18 through various means that include MCAScontrol panel 30, control display unit 37, and data transfer system 38.The utility of the input data is to indicate mode selections to thesystem, activate specific mission capabilities, signal formation flightevents, and report the progressive stage of a mission. The MCAS 18evaluates this information to determine system mode. The input data toMCAS 18 can include, but not be limited to:

selected operational mode—ATM, Tactical, or Mixed

formation flight mode

aircraft role in a formation flight—leader, sub-leader, or wingman

specified vertical, longitudinal, and latitudinal offsets

rendezvous mode

aircraft role in a rendezvous/air-refueling—tanker or a re-fueller

rendezvous position and time

transitional event from rendezvous to air-refueling

arm and disengage air refueling

own aircraft identification (ID)

identification of other interested aircraft

mission identification (MID)

aircraft data—latitude, longitude, altitude, airspeed for test mode

display scales for 10, 20, 30, 60, 90-second radius

Intruder track file correlation process 54 performs temporal intruderdata based on time tagged with a precise universal time provided by theGlobal Position System (GPS) segment to provide a currency of intrudertrack file. It is important to note that since CAS data comes from manydifferent sources (Mode S/IFF, digitized tactical data link, airborneradar, and etc.), it is necessary that this data be correlated in termsof mission ID, aircraft ID, or flight number. This is to ensure that thedata coming from the same aircraft will be blended in the block 56 andused in processing collision avoidance solutions 58 and 60, formationflight control and guidance 62, air-refueling control guidance 64, andMCAS display drivers 68.

Blending sensor data process 56 uses a complementary filtering techniquewith some average weighting factors to combine the computed bearing anddistance from the Mode S/IFF and, digitized tactical data link with theraw bearing and distance provided by the airborne radar 36 and stationkeeping equipment 37. This information is used in generating displayimages for traffic situation and selection of intruders in range fordisplay.

The display driver (e.g., NVS, MFD, and HUD) 68 provides video, digitaldata, and digital image data to drive night vision system (NVS),multi-function display (MFD), and heads-up display (HUD) system whilethe display driver 76 in the ATM module 20 has the capability to drive acommercial vertical speed indicator and traffic-resolution advisory(VSI/TRA) color display unit and electronic flight instrument system(EFIS).

Tactical traffic alerts process 60 uses the tactical model defined inFIG. 9 to determine if an intruder aircraft is in an advisory, caution,or warning situation and generate appropriate display messages, symbols,and audio to warn of the level of danger detected in an air proximitysituation.

Tactical collision avoidance resolution process 58 evaluates theprocedure that a host aircraft has to follow if the intruder aircraft isin caution air space and about to penetrate the warning (collision) airspace. The process of selecting specific maneuvers and performing flightpath re-planning will be a function of aircraft dynamics and the flightpath characteristics of the intruder aircraft and the host aircraft asshown in FIG. 10 and FIG. 11.

Formation flight advisory and guidance process 62 continuously computesthe desired wingman position based on the current position of theformation leader and the offset values. The process 62 then computes thelateral deviation, longitudinal deviation, vertical deviation, relativevelocity, and relative acceleration. These parameters are input to theflight guidance control laws to generate roll commands, vertical speedcommands, and thrust commands that are used to drive flight directorcues and couple with a flight control system. If the aircraft is aformation leader or sub-leader, then any CAS advisories and resolutionsthat are currently active by direct (leader) or indirect (sub-leader)generation are made available to the wingmen, along with maneuveringevents such as start-climb, start-descend, roll-in, roll-out, level-out,and etc. The process 62 determines all the maneuver events if theaircraft is a leader in a formation flight.

Rendezvous and air-refueling advisory and guidance process 64 computesthe distance and estimated arrival time at a rendezvous position. Thisinformation is maintained and complemented with the contact data (dataestablished through digital data link that provides informationregarding the aircraft system parameters of the host aircraft). When theair-refueling phase becomes active, the process 64 performs similarcomputations as in process 62 to calculate guidance commands to maintainair re-fueling and relative docking, position and generate advisories ifany deviations exceed thresholds.

RF power and transmission management 66 provides a capability to managetransmission power levels of RF radiating sources and the transmissionrate for equipment operating in a particular RF spectrum. Referringagain to FIG. 2, equipment in this group includes a Mode-S/IFFtransponder 32, airborne radar 36, Station Keeping System (SKE) 36, andany tactical radios that might be used to support the digitized tacticaldata link 34. The system monitors pilot selection to control powersetting levels for the equipment, and periodically schedules fortransmitting data per request, requesting tactical/mission data, or justbroadcasting. If the pilot selects to operate in a silent mode, then thesystem will inhibit all transmission activities, but will continue tooperate in a passive mode by purely receiving data from the IFF extendedMode S and digitized tactical data link 34 to provide CAS solutions.MCAS voice and tone generation process 67 is based on priority settingfor caution, advisory, and warning events to generate specific tone andvoice messages associated with the event. The process 67 also monitorsthe removal of events or acknowledgment from the flight crew in order todistinguish tone and voice generation.

Referring to FIG. 5, there is shown a logic flow in determining theactive mode for the MCAS 18, which is performed in MCAS controlmanagement 50. After system power-up, the first functions initiated aresystem initialization process and power-up built-in-test (PBIT). Due totime rate scheduling, the first check in the logic flow is determined ifMCAS power-up BIT has been completed at step 100. If PBIT is still inprogress, then the logic evaluation process is terminated in step 100.Otherwise, the next test is performed at step 102 to determine if thisis very first time this logic has been evaluated since the PBIT iscomplete. To determine if one of the three system modes (ATM, tactical,or mixed) can be set to active, the system obtains internal BIT results,and BIT results from other equipment such as IFF Mode S transponder anddigitized tactical data link at step 104. If MCAS has no criticalfailure at step 105, then the IFF Mode S transponder BIT results isevaluated at step 106. If there is no critical failure in the IFF mode Stransponder, the system then tests for any critical failure in thedigitized tactical data link in steps 122 and 108. If there is nofailure in either the IFF mode S transponder and digitized tactical datalink, then the mixed mode is set to active at step 128. If only the IFFmode S transponder is healthy, then the ATM mode is set to active atstep 126. If only digitized tactical data link is active, then tacticalmode is set to active at step 124. After setting one of the modes toactive, MCAS control and management 50 sets start-up phase signal to atrue state at step 130. With this signal being set, in the next frametime, the system follows the path to process mode transition logicdefined in step 120 in order to evaluate system mode for subsequent tosystem start-up. The logic flow of step 120 is outlined in more detailin FIG. 6.

Referring to FIG. 6, there is shown a state transition diagram providingnecessary logic to allow a transition from one system mode to anothersystem mode. If the current system mode is the Mixed mode 150, then thesystem evaluates all logical conditions defined in blocks 152 and 154.If the conditions in block 152 are met, the system makes a transitionfrom the Mixed mode 150 to the ATM mode 170. Otherwise, if theconditions in block 154 are met, then the system will make a transitionfrom the Mixed mode 150 to the tactical mode 160. If the current mode isthe tactical mode, then the system will evaluate logical conditionsdefined in blocks 162 and 164. If the conditions in block 162 are met,the system makes a transition from the tactical mode 160 to the ATM mode170. If the conditions in block 164 are met mode, the system makes atransition from tactical mode 160 back to the Mixed mode 150. If thecurrent mode is the ATM mode 170, then the system evaluates logicalconditions defined in blocks 172 and 174. If the conditions in block 172are met, the system makes a transition from the ATM mode 170 to thetactical mode 160. If the conditions in block 174 are met, the systemmakes a transition from ATM mode 170 back to the Mixed mode 150.

Referring to FIG. 7, there is shown a block diagram to furtherillustrate the structure of MCAS mission and user data process 53 andtactical communication protocols 51. In order for the MCAS to operatewith a full capability, MCAS obtains and processes data from a varietyof external sources. Within the block 53, block 200 (process MCAS datafrom data transfer system) requests and down loads the mission relateddata (e.g., aircraft ID, mission ID, flight number, identification ofother interested aircraft, rendezvous position and time, relativeposition offsets for formation flight, and etc.). Subsequently, if anyof the listed parameters has been changed by manual data entry via thecontrol display unit (CDU) 37, the process 53 provides utility totransmit/store the data back to the CDU. Outputs from this process 200are MCAS preset data 240 for use by intruder track file correlationprocess 54 and platform/mission specific data 246 for use by processtransmitter digitized tactical data link messages 206.

Referring to FIG. 8, there is shown a logic flow diagram to show thetrack file data correlation and the process of blending sensor data. Thepresent invention provides a graceful degradation for all modes ofoperation. The system provides logic to select the best possible sensordata for CAS computations. The complementary data from DigitizedTactical Data Link 34, Airborne Radar 36, and Station Keeping Equipment(SKE) 36 is used to enhance the primary IFF Mode S/Transponder 32 data,fill any data gaps, or serves as back-up. The computed range and bearingdata from the digitized tactical data 34 is combined with that of theIFF “Diversity” transponder whenever the data is available and valid.The blended information is used to determine if another aircraft is inthe caution region, warning region, or about to penetrate the collisionregion. To perform this process, the system obtains the information ofits own aircraft present position and present altitude in block 250. Theinformation pertaining to the position and pressure altitude of eachintruder aircraft is provided by digitized tactical data link system inblock 252. The system ensures that each record of each intruder aircraftis processed in step 254. In block 256, range and bearing angles fromthe host aircraft relative to each intruder are computed. If thetransponder also provides data for a correlated aircraft in step 258,then the system uses a complementary filter method to provide a betterestimate of range and bearing values in step 260. Otherwise, the systemchecks to determine if the station keeping data for a correlatedaircraft is available in step 262. If it is available, then the systemuses a complementary filter method to provide an estimate of distanceand bearing from the two sources of input data in step 264. If data arenot available from IFF transponder and station keeping equipment, thenanother test is performed to determine if airborne radar data isavailable in step 266. If airborne data is available, then the range andbearing computed from digitized tactical data link will be correlatedwith the range and bearing data generated by the airborne radar systemin step 268. If there is a match in the data correlation process, thenthe system uses a complementary filter method to provide an estimate ofrange and bearing from the two sources of digitized tactical data linkand airborne radar in step 272.

Referring to FIG. 9, there is shown a multi-dimension tactical aircraftand collision model used to evaluate aircraft proximity in terms ofclosure range and closure rate to determine relative time spaceseparation. In the mixed mode, MCAS 18 uses a different time-baseddimension model than the ATM mode to track tactical aircraft anddetermine air traffic and collision avoidance situations. The tacticalmode has three distinctive advisory, caution, and warning air spacesbeing equally distributed in three-dimensional space and time toincrease situation awareness and probability of avoiding air collision.In addition, warning and caution air spaces are set with tighter timeconstraints than the ATM mode, that is not only to minimize nuisancewarnings but to reflect the level of lethality of an air collision in atactical environment.

In the Tactical mode, the MCAS 18 determines if the aircraft's currenttrack being projected will intersect with the track of an intrudertrack. The MCAS 18 then monitors a time-based dimension model asillustrated in FIG. 9 with three CAS influence spheres (80, 82, 84). Theinner sphere 80, which is defined as a highest probability of aircollision—warning sphere, extends from the aircraft equipped with MCASto an intruder aircraft within about 10 seconds before two aircraftconverge to a collision point in midair. The middle sphere 82, which isdefined as a medium probability of air collision—caution sphere, isextended with an additional 15 seconds time from the warning sphere. Ifan intruder penetrates the boundary of the warning sphere, an escapestrategy in the form of a tactical avoidance resolution advisory (RA)such as evasive maneuvers guidance (climb, descend, climb and turn, ordescend and turn) will be generated to guide the pilot. If required, theguidance command can be selected to couple with a flight control system.The RA is a vertical maneuver and/or a lateral maneuver based onvertical situation with respect to other aircraft in the proximityairspace and clearance of local terrain situation projected formaneuvering flight path as shown in FIG. 11. MCAS monitors a time-baseddimension of an advisory sphere 84 that extends from 35 seconds up to 50seconds from the time the intruder enters the MCAS aircraft's warningregion 80. The closure time is calculated based on the line-of-sightdistance from the reference aircraft to the intruder aircraft and thecalculated closure rate if the closure rate is positive. If thecalculated closure rate is close to zero, then the closure rate is setequal to a value of 5 Nautical Miles per hour to avoid any singularityin closure time computations. If the closure rate is a negative value,then the reference position (host aircraft) and the intruder are movingaway from each other. The closure rate is the difference between thevelocity vector of the host aircraft 85 and the velocity vector of theintruder aircraft 86 being projected on the line of sight vector 87. Inthe event that the velocity component is not available, then anestimated closure rate will be derived from the line of sight distanceand its update rate through a moving average filter. If the aircraft iseither a formation leader, a sub-leader or a tanker, then MCAS 18 willsend ATM TAs and RAs and tactical TAs and RAs to wingmen (followeraircraft) and refueler aircraft for display and guidance controlprocessing.

Referring to FIG. 10, there is shown a logic flow diagram fordetermining corrective maneuvers to avoid an air collision situation ina mixed mode operation. When the intruder aircraft is in a caution airspace 82 as shown in FIG. 9, then the tactical collision avoidanceresolution 58 begins to predict the necessary maneuvers for the hostaircraft. The control and guidance for avoidance maneuvers areinstantaneously provided to the pilot with flight director commands andflight control commands. This process reads the predicted flight phasedata for both the host and intruder aircraft in step 300. A test todetermine whether if both aircraft are in a climbing phase is performedin step 302. If both aircraft are in a climb phase, then block 304 willbe processed. The aircraft with a higher-pressure altitude will increasevertical speed to an allowable level until the air collision conditionis clear while the aircraft with a lower pressure altitude will reducevertical speed if the terrain situation allows for it. If both aircraftare not in a climb phase, then the test 306 will determine if oneaircraft is in a climb phase while another aircraft is in a descendphase. If the condition is met, then block 308 is processed. In block308, if the aircraft in descent has a higher pressure-altitude, thenflight path re-planning has to be performed as shown in FIG. 11.Otherwise, if the aircraft in climb has a higher-pressure altitude, theabsolute vertical speed from each aircraft will be increased. The nexttest 310 is to determine if one aircraft is in climb and anotheraircraft is in level flight. If the condition in 310 is met, block 312will be processed. If the aircraft in climb has a lower pressurealtitude than the aircraft is in level flight, then the aircraft inclimb will have to level out and the aircraft in level flight will needto initiate a climb. If the aircraft in climb has a higher-pressurealtitude than the aircraft in level flight, then the aircraft in climbwill have to increase the climb rate until air collision condition isclear and the aircraft in level flight will initiate a descent ifterrain is also clear. The next test 314 is to determine if one aircraftis in level flight while another aircraft is in descent. If thecondition in 314 is met, block 316 will be processed. In this block 316,if the aircraft in level flight has a lower pressure altitude than theaircraft in descent, then the aircraft in level flight will have toinitiate a descent if terrain situation is allowed and another aircraftwill have to level out. The next test 318 is to determine if bothaircraft are in level flight. If the condition in 318 is met, block 320will be processed. In this block 320, the aircraft with a lower-pressurealtitude will decend at a rate that can obtain terrain clearance and theaircraft with a higher-pressure altitude will initiate a climb. Bothaircraft will return to their previous altitude when the air collisioncondition is no longer valid. The next test 322 is to determine if bothaircraft are in decent. If the condition 318 is met, block 324 will beprocessed. In this block 324, the aircraft with a higher-pressurealtitude will level out and another aircraft will increase its descentrate if local terrain situation is permitted.

Referring to FIG. 11, there is shown a flight situation where it isnecessary to re-plan the current flight segment to avoid a mid aircollision situation between the host aircraft 350 and an intruderaircraft 352. The system will process the situation with an initialright turn 358 and determine if the local terrain 362 that correspondswith this proposed flight path is clear from the proposed vertical path.If this flight path does not have a terrain clearance, then a symmetrypath 356 will be evaluated for both air collision and terrain clearance364. Different turn angles will be used to find the lateral path. Whenthe air collision condition is no longer valid, the aircraft will changeits maneuver to re-capture the original flight path.

Referring to FIG. 12, there is shown a block diagram to provide logicand computations performed for each member in a formation flight. Thefirst step 400 is to determine if the formation flight is active. If theformation flight is active, the system will process the information suchas the role of the aircraft in a formation, preset data such as relativeposition offsets in x, y, and z axes, and dynamics coordinated tacticalinformation in block 402. In step 410 a test is performed to determineif the aircraft is set as a main formation flight leader 409. If it is,then the system processes flight dynamics data to determine maneuveringevents (e.g.; begin to turn, turn left, turn right, begin to climb,begin to descend, and etc.) to signal to the follower aircraft. In thenext block 414, the system collects and formats data into packets thatwould be needed by the follower aircraft. In step 420, if the systemdetermines that the aircraft is not a main leader but a sub-leader 419in a formation flight 420, then the system will process the informationassociated with ATM/tactical traffic advisories and resolutionadvisories provided by the leader aircraft. In step 422, the system willuse the navigation data from the host aircraft as well as the leaderaircraft to determine relation position errors based on the presetrelative offset values. With the computed relative position errors, thesystem feeds this information to the guidance control process todetermine pitch, roll and thrust commands for error correction. In block422, the system also determines whether to engage or disengage theformation flight mode. In block 426, the system monitors the positiondeviations against the upper as well as lower thresholds to triggerdifferent formation flight advisories. The next block 428 is to collectand process formation flight data packet to transmit to the followeraircraft. If step 420 is a no, then the test 430 is to determine if theaircraft is a wingman 429. If it is, then block 432 is processed. Thesystem processes the information related to ATM and tactical trafficadvisories and collision resolution provided by the leader as a part ofsituation awareness display information. At the same time in step 432,the system in the wingman calculates relative position errors in orderto feed this information to the guidance control process for generatingpitch, roll and thrust correction commands and formation mode state instep 434. In this step, the system also monitors maneuvering commandfrom the leader aircraft in order to compute delayed time and that willdetermine when the wingman should initiate a similar maneuver. In step436, the system also compares the position deviations against specifiedthresholds to generate formation flight advisories such as: unable tokeep up with the formation flight designation or exceeding lowerthreshold limits. As in the event of information flight break-away, thesystem will determine target roll angle command and target air speed tofeed to the control guidance based on the aircraft relative position ina formation. An example for this is that the first right wingman willinitiate a 30 degrees right hand turn and reduce 10 knots in airspeedand his follower wingman will initiate a 60 degrees right hand turn andreduce 20 knots in airspeed.

Referring to FIG. 13, there is shown a logic flow diagram illustratingthe processing for tanker 490 and air re-fueller aircraft 492 in variousphases of an air-refueling mission. The system can allow both the tankerand the refuellers to maintain precise situation awareness during allphases of the operation. The MCAS displays range, bearing, and relativealtitude. These key parameters can be used to identify another aircraftor formation element relative location and hence improve the efficiencyand mission times for in-flight rendezvous events. The advantage forrendezvous using digitized tactical data link is relative position,range, and arrival time can be displayed more accurately. Relative rangeand bearing will be calculated by MCAS based upon GPS positionbroadcasting by the Mode S transponder or received by digitized tacticaldata link system. When making close encounters with other aircraft forrendezvous purposes, the MCAS equipped aircraft will inhibit tacticaltraffic and resolution advisories and allow transition to anair-refueling mode to take place. The system checks to determine ifrendezvous/air-refuelling mission is selected in step 450. If it is, thesystem obtains aircraft role in the mission along with the rendezvousposition 494 in block 452. Next step 454 is to determine if the aircraftis a tanker. If it is, the system calculates distance, bearing angle andestimate time of arrival to the rendezvous position, which is thecontrol point of the tanker orbit in step 456. The system also searchesin the intruder track file for the air-refueller aircraft identificationto determine if the air-refueller aircraft is within the contact rangein step 458. The next test 460 is to determine if the air refuelleraircraft is linked up to begin the refueling phase. If it is, the tankeraircraft control guidance syncs up with the air speed of theair-refueller aircraft in step 462. If it is not, the system preparesrendezvous and air refueling data packet for transmission in step 464.If the test in step 470 determines that the host aircraft is anair-refueller, then the system performs another test 472 to verify theaircraft is in docking phase. If the air-refueller is in docking phase,the system will command the control guidance to sync up with the tankerair speed in step 480. While in the re-fuelling phase, the systemcalculates relative position deviations in step 482 and feeds thisinformation to control guidance to provide correction commands in step484. If the air-refueller aircraft is not yet in docking phase, thesystem will compute distance, bearing angle and estimate time of arrivalto the initial point (IP) and control point of tanker orbit in step 474.The system monitors based on surveillance to determine if the tanker isin range in step 476. The last step 478 is to prepare rendezvous and airre-fuelling data packet for transmitting.

Referring to FIG. 14, there is shown a logic flow diagram which outlineslogical conditions to determine appropriate power level required to beset for RF radiating sources. These sources include mode S/IFFtransponder, tactical radios (e.g., ARC-201D, ARC-220, or any tacticalVHF/UHF), station keeping equipment and airborne radar). The first step500 in this functional module is to get information regarding aircraftrole as well as pilot command for power setting for RF equipment. Instep 502, if the electromagnetic communication mode is set to silent,then the system will set equipment to the standby mode and turn offtransmission power in step 504. If the silent mode has not been set,then another test 506 is involved to determine if the override mode forpower setting is active. If it is, the system sets transmission powerfor RF equipment per pilot setting in step 508. The next test 510 is todetermine if the aircraft is a sub-leader in a formation flight or atanker in re-fuelling phase. If test 510 is true, then the system settransmission power for RF equipment to lower power level or leakagelevel in step 512. If the test 514 determines that the aircraft iseither a wingman aircraft or an air-refueller in refuelling phase, thesystem sets the transmission power for RF equipment to a leakage levelin step 516. Otherwise, the system sets RF equipment to a nominal(medium) power level in step 518.

Referring to FIG. 15a, there is shown a display format of traffic andair collision situation in ATM mode with a complement of tacticalaircraft 550 and 554 detected through digitized tactical data linkmedium and ATM aircraft 552 and 556 detected by the IFF Mode Stransponder.

Referring to FIG. 15b, there is shown a display format of traffic andcollision situation in a mixed mode. The information of air traffic andavoidance information generated from the airborne radar system andstation keeping 562 is combined with the traffic information processedby the IFF transponder, such as 552 and 556, and the tactical digitizeddata link system, such as 550 and 554.

Referring to FIG. 15c, there is shown a display format of tacticalsituation awareness provided by the formation leader being overlaid withthe position error 574 and relative velocity 572 with respect to theformation leader aircraft.

Other variations and modifications of the present invention will beapparent to those of skill in the art, and it is the intent of theappended claims that such variations and modifications be covered. Theparticular values and configurations discussed above can be varied andare cited merely to illustrate a particular embodiment of the presentinvention and are not intended to limit the scope of the invention. Forexample, the antenna mounting technique taught in U.S. Pat. No.5,805,111 could be implemented in the present invention to extend TCASdetection range. Further, the present invention further comprises adigital terrain elevation database that allows the TCAS to generate avertical terrain profile, which results in a survivable control andguidance system. It is contemplated that the use of the presentinvention can involve components having different characteristics aslong as the principle, the presentation of a TCAS with a tactical basedmodule, is followed. The present invention applies to almost any CASsystem and is not limited to use by TCAS. Additionally, although thepresent invention has been described with respect to aircraft operatinga military tactical environment, it has application to aircraftoperating in a civilian/commercial air space. It is intended that thescope of the present invention be defined by the claims appended hereto.

What is claimed is:
 1. A method for avoiding collisions when operatingan aircraft comprising: operating in a first mode when in an air trafficcontrol environment; operating in a second mode when in a tacticalenvironment; and operating in a third mode when in a mixed air trafficcontrol/tactical mode.
 2. A midair collision avoidance system for use inan aircraft, the system comprising: an air traffic management modulethat tracks objects when the system is operating in an air trafficcontrol mode; a tactical based management module that tracks objectswhen the system operating in a tactical control mode; and wherein theair traffic management module and the tactical based management moduleboth track objects when operating in a mixed air trafficcontrol/tactical mode.
 3. The system of claim 2, further comprising aninternal communication link coupling the air traffic management moduleand the tactical based management module, the internal communicationlink passing data between the the air traffic management module and thetactical based management module.
 4. The system of claim 3, wherein theair traffic management module includes a first data bus, the tacticalmanagement module includes a second data bus, the first data bus coupledto the second data bus by the internal communication link.
 5. A systemfor operating an aircraft in the vicinity of other objects, the systemcomprising: a midair collision avoidance system that tracks a firstobject external to the aircraft in an air traffic control environmentand a second object external to the aircraft in a tactical controlenvironment; and a transponder coupled to the midair collision avoidancesystem, the transponder receiving information regarding the first andsecond objects external to the aircraft and supplying the information tothe midair collision avoidance system.
 6. A midair collision avoidancesystem for use in an aircraft, the system comprising: an air trafficmanagement module that monitors and tracks objects in an air trafficcontrol environment; and a tactical based management module, incommunication with the air traffic management module, that monitors andtracks objects in a tactical environment.
 7. A midair collisionavoidance system for use in an aircraft, the system comprising: an airtraffic management means for tracking objects when the system isoperating in an air traffic control mode; a tactical based managementmeans for tracking objects when the system operating in a tacticalcontrol mode; and wherein the air traffic management means and thetactical based management means both track objects when operating in amixed air traffic control/tactical mode.
 8. The system of claim 7,further comprising an internal communication means coupling the airtraffic management module and the tactical based management module, theinternal communication means for passing data between the the airtraffic management module and the tactical based management module. 9.The system of claim 8, wherein the air traffic management means includesa first data bus, the tactical management means includes a second databus, the first data bus coupled to the second data bus by the internalcommunication means.
 10. A system for operating an aircraft in thevicinity of other objects, the system comprising: a midair collisionavoidance means for tracking a first object external to the aircraft inan air traffic control environment and a second object external to theaircraft in a tactical control environment; and a transponder meanscoupled to the midair collision avoidance system, the transponder meansfor receiving information regarding the first and second objectsexternal to the aircraft and for supplying the information to the midaircollision avoidance system.
 11. A midair collision avoidance system foruse in an aircraft, the system comprising: an air traffic managementmeans for monitoring and tracking objects in an air traffic controlenvironment; and a tactical based management means, in communicationwith the air traffic management module, for monitoring and trackingobjects in a tactical environment.